1. Field Of The Invention
This invention relates to novel phosphorylated reaction products and, more particularly, to novel products for use in compositions such as magnetic recording media for enhancement of the dispersion and magnetic property characteristics of such medium.
2. Description Of The Prior Art
Over the years, magnetic recording has come to occupy a vital place in a myriad of industries. Magnetic tape is accordingly utilized for audio, video, computer, instrumentation and other recordings. Magnetic recording media are utilized in a variety of forms, including, for example, magnetic cards and disks, reels, video tapes, high performance audio tapes, computer tapes, floppy disks, and the like.
While there are several different types of magnetic recording media, all types comprise a layer of magnetic particles, sometimes referred to as "pigment," coated on a plastic, paper or metal base. Information to be recorded is stored in the magnetic pigment as a series of small domains magnetized by a recording head. The coating layer of the magnetic medium includes a binder system which provides a cohesive matrix between the magnetic pigment particles and adheres such particles to the base.
The magnetic coating is applied to the base by coating equipment such as, for example, a gravure roll coater, and the coated base then typically immediately proceeds to a magnetic orientation step wherein orientation of the pigment particles is effected on the undried layer. In this step, the long axis of the pigment particles, typically acicular crystals, is made to coincide with the magnetization direction.
In order to achieve good recording performance, the magnetic coating must possess a wide variety of characteristics. Pigment particles, desirably of relatively uniform particle size, should form as high a proportion of the coating layer as possible. Further, the degree of dispersion of the pigment particles in the coating, often evaluated as degree of gloss, should be as high as possible. Further, the highly dispersed pigment particles must be capable of being adequately oriented, as previously described (the degree of orientation often measured as "squareness").
Still further, the adhesion and wear resistance of the magnetic coating or film should be high. Also, the coefficient of friction of the magnetic surface should be low against the recording and playback head material, and yet have an adequate value against the driving means, such as pinch rollers and capstan rollers.
Satisfying these and other diverse criteria has proven to require a delicate balance of basically reciprocal, or opposing, properties. A substantial amount of effort over the years has been directed to improving the various characteristics of magnetic recording media.
To satisfy the performance criteria, the binder system must possess adequate modulus, yet have satisfactory tensile strength and resilience. It has generally been found more desirable to satisfy these criteria by utilizing more than one material in the binder system. Typically, a polymer of relatively high molecular weight which is capable of being cross-linked or cured is utilized to provide the desired modulus. Various elastomers are also incorporated to achieve the desired resilience and toughness.
Conventional binder systems include a wide variety of high Tg (viz., glass transition temperature) hardening polymers or resins, such as, for example, polyacrylates, polyesters, polyester amides, polyhydroxyethers and copolymers from monomers such as vinyl chloride, vinyl acetate, acrylonitrile, vinyl alcohol, vinyl butyral, and vinylidene chloride in combination with low Tg elastomeric polymers, including nitrile rubbers, polyesters, alkyd resins and polyester polyurethanes. The latter elastomers often represent the material of choice for high performance applications. Such resins have excellent toughness and abrasion resistance.
Typically, the hardening polymers contain hydroxyl functionality since cross-linking to further increase the modulus, durability and abrasion resistance characteristics can then be achieved by using polyfunctional isocyanates. While satisfactory cross-linking can be achieved with polyfunctional isocyanates, such materials are notoriously sensitive to moisture, which can cause problems. Also, cross-linking occurs over a period of time, including while the magnetic recording medium, is in storage. Premature cross-linking may also make calendering of the recording medium difficult or impossible.
It would accordingly be desirable to provide a binder resin capable of being cured or cross-linked by electron beam radiation techniques. Various electron beam curable, multifunctional acrylates and methacrylates are known. The difficulty is the method by which such materials may be utilized since these materials have mechanical properties and surface wear resistance characteristics that are generally considered inadequate for magnetic coatings.
The degree of dispersion and the capability of the pigment particles to be oriented in many binder systems are often considered inadequate in the absence of dispersion aids. A wide variety of techniques have been proposed to improve these characteristics. Thus, many surface active agents have been employed for this purpose. These include higher aliphatic amines, higher fatty acids, phosphoric acid esters of higher alcohols such as polyoxyethylene phosphate alkyl ethers, esters of higher fatty acids and sorbitol, sodium alkylbenzenesulfonate, betaine-type, nonionic surface active agents and the like.
Magnetic coatings obtained by employing such surface active agents generally exhibit uniform dispersion of magnetic powder as well as good orientation where the powder or pigment is in the form of acicular particles. On the other hand, utilization of such agents often adversely affects wear resistance or causes difficulties in quality during use. These problems are often attributed to migration or blooming of such surface active agents to the magnetic coating surface or to unnecessary plasticization of the hardening resin or of other components in the magnetic coating.
One attempt to obviate the migration problem is suggested by Great Britain Patent 2,097,415A. This suggests using with a cross-linkable or polymerizable resin binder a phosphoric acid ester having at least one polymerizable unsaturated double bond. Preferably, the phosphoric acid ester is a product obtained by reacting a phosphoric acid ester of a compound having two or more hydroxyl groups with an acrylic or methacrylic compound having a functional group reactive with an isocyanate group and also with a polyisocyanate compound. The phosphoric esters disclosed include two major types: (1) the reaction products of a long chain alkylether or polyester, an acrylic or methacrylic compound having a functional group reactive with an isocyanate group, and a polyisocyanate compound and (2) phosphoric esters of hydroxyalkyl acrylates.
Other binder systems disclosed utilize compounds including various hydrophilic groups such as sulfates, sulphonates, phosphonates and the like. Japanese application 116,474 discloses a magnetic layer binder composition of a polyurethane and optionally a polyester containing sulphonate groups, and a vinyl chloride polymer containing sulphonate, sulphate, carboxylate or phosphonate groups. The binder is stated to have good dispersing function to magnetic powder and the recording medium to have excellent service durability and good surface gloss.
Japanese Patent J57092421-A(8229) discloses a magnetic recording medium which includes a polyester urethane having (1) at least one hydrophilic group such as --SO.sub.3 M, --OSO.sub.3 H, --COOM, --P(O)(OM').sub.2, --NH.sub.2, --NHR, NR.sub.1 R.sub.2, and NR.sub.1 R.sub.2 R.sub.3, wherein M may be H, Li, Na or K; M' may be H, Li, Na, K or a hydrocarbon group; and the R groups may be a hydrocarbon group and (2) at least two acrylic-type double bonds.
Japanese J57092422-A(8229) discloses a magnetic layer containing a polyurethane or polyester resin having (1) at least one hydrophilic group selected from --OSO.sub.3 H, --COOM, --P(O)(OM').sub.2, wherein M may be H, Li, Na, or K and M' may be H, Li, Na, or K or a hydrocarbon group, and (2) a molecular weight of 200 to 5000 per hydrophilic group.
International Publication No. W08400240-A discloses a magnetic recording medium containing a polyvinyl chloride-vinyl acetate-vinyl alcohol and a polyurethane resin containing polar groups such as --SO.sub.3 M, --OSO.sub.3 M' --COOM or ##STR1## wherein M and M' are as defined above and M.sub.1 and M.sub.2 may be Li, Na, K or an alkyl group, preferably an alkyl group with up to 23 carbon atoms.
Japanese J55117734-A(8043) discloses a binder for a magnetic recording medium which contains a copolymer of a phosphoric acid ester of an alkylene glycol acrylate or an alkylene glycol methacrylate and a copolymerizable monomer. The wetting properties to ferromagnetic material is stated to be very good, so that dispersibility in the binder is improved. Blooming is said not to occur as no high aliphatic acid, metallic soap, or the like is used.
Among the binder polymers in use in magnetic coating media are commercially available, partially hydrolyzed, (viz., partly saponified) vinyl chloride-vinyl acetate copolymers and terpolymers and phenoxy resins. For the highest performance applications, such as computer tapes, floppy disks and the like, phenoxy resins are often the binder resin of choice because of the superior durability, toughness and thermal stability that is provided.
Unfortunately, the dispersion and orientation characteristics of coatings utilizing such binder polymers are typically less than is desired. Considerable efforts have been undertaken to improve these characteristics with the use of a wide variety of dispersion aids.
U.S. Pat. No. 4,420,537 to Hayama et al. thus discloses a magnetic recording medium including a commercially available vinyl chloride-vinyl acetate-vinyl alcohol copolymer and a phosphoric ester-type anionic surfactant (e.g., "GAFAC RE 610"). It is noted that when the content of the surfactant is more than 5 weight percent of the coating, the surfactant is bloomed out from the magnetic layer.
U.S. Pat. No. 4,153,754 to Huisman notes difficulties with prior dispersing agents. Low molecular weight agents, such as lecithin, have the disadvantage that an excess is necessary to fully cover the particles to be dispersed. The high molecular weight dispersing agents, as described, for example in Netherlands Patent Application No. 65.11015, have the disadvantage that, due to their poor wetting properties, agglomerates of the particles are also covered with a dispersing agent. It is not readily possible, or it is possible only by the use of much energy, to disintegrate such agglomerates to individual particles. Huisman suggests using an N-acylsarcosine derivative as a dispersing agent with the binders. The Examples show use of such a dispersing agent with a commercially available phenoxy resin and a vinyl chloride-vinyl acetate-vinyl alcohol terpolymer.
U.S. Pat. No. 4,291,100 to Horigome et al. discloses a magnetic recording medium utilizing a polyoxyethylenesorbitane higher fatty acid ester surfactant. The Examples include use of such surfactants with vinyl chloride-vinyl acetate copolymers and vinyl chloride-vinyl acetate-vinyl alcohol terpolymers.
U.S. Pat. No. 4,305,995 to Ota et al. shows a magnetic recording medium including a mixture of sorbitane mono-, di-, and tri-higher fatty acid ester surfactants. The Examples show use of such surfactants with vinyl chloride-vinyl acetate copolymers.
U.S. Pat. No. 4,330,600 to Kawasumi et al. discloses a magnetic recording medium in which the dispersion characteristics of magnetizable particles are improved which results in improved saturation magnetic flux density and squareness ratio. These are achieved by treating the magnetizable particles with a titanium alcoholate compound having at least one group which is easily hydrolyzed and at least one oleophilic group which is hard to hydrolyze in an organic solvent. The Examples show use of such titanium alcoholates with a commercially available vinyl chloride-vinyl acetate copolymer binder.
U.S. Pat. No. 4,400,435 to Yoda et al. notes that vinyl chloride-vinyl acetate copolymers have been used as binders, but that such copolymers do not have functional groups whereby it is easy to improve the dispersibility of magnetic powder in a magnetic layer. It is further said that it is not easy to carry out a thermosetting reaction. The use of vinyl chloride-vinyl acetate-vinyl alcohol copolymers instead had been proposed; and, because of the hydroxyl groups present, the dispersibility of magnetic powder is improved and the thermosettable reaction can be performed. However, because of the vinyl alcohol component, the glass transition temperature of the copolymer is disadvantageously high so as to provide difficulties in improving the surface properties by a calendar process. A magnetic recording medium having improved orientation and maximum residual magnetic flux density is provided by using a vinyl chloride-vinyl acetate-maleic acid copolymer having a content of the maleic acid component of at least 1.5 percent.
In addition to the problems of providing a binder system in which the pigment particles can be highly dispersed to form a magnetic coating in which such particles can then be readily oriented in the first instance, the manner of usage can create further problems. Thus, achieving adequate dispersion requires use of relatively high energy mixing equipment. As one example, a mixture of the binder system in a solvent is provided, and the mixture is then thoroughly kneaded and agitated on a 3-roll or high speed agitation mixer or kneader. The resulting slurry is then often transferred to a ball mill, sand grind mill or other dispersion equipment to achieve an even higher degree of dispersion of the magnetic particles in the coating.
If the coating is used rather promptly after formation, no problem results. However, as is sometimes the case, usage requirements may dictate that the coating mixture be stored. Such storage can result in substantial decay of the advantageous dispersion characteristics originally achieved. The use of such "stale" coating mixtures thus presents problems as regards the processing required to allow the pigment particles to attain the desired orientation when such coating mixtures are used and processed. It is obviously economically undesirable to be forced to repeat the initial, high energy mixing sequence.
Accordingly, despite the considerable prior effort in this field, the need remains for a straightforward solution that will allow use of otherwise desirable binders to achieve the desired dispersion and orientation characteristics over a widespread variety of usage requirements.